Find the sum
`Sigma (3n^2+2n)`

Find the sum Sigma_(j=1)^(n) Sigma_(i=1)^(n) I xx 3^j

Find the sum Sigma_(r=1)^(n) 1/(r(r+1)(r+2)(r+3)) Also,find Sigma_(r=1)^(oo) 1/(r(r+1)(r+2)(r+3))

Find the sum Sigma_(r=1)^(n) r/((r+1)!) . Also, find the sum of infinite terms.

Find the sum Sigma_(r=1)^(oo)(3n^2+1)/((n^2-1)^3)

Let sigma(n) denotes the sum of digits of a natural number n .If N is the smallest natural number such that sigma(N)=2020 , then find the value of sigma(5N+2021)

Find the sum: (n^(2)-1^(2))+2(n^(2)-2^(2))+3(n^(2)-3^(2))+...+n(n^(2)-n^(2))

Find the rth term of an AP, the sum of whose first n terms is (3n^(2) +2n)

Find the sum sum_(n=1)^(oo)(6^(n))/((3^(n)-2^(n))(3^(n+1)-2^(n+1)))